Simple Pretreatment and HILIC Separation for LC-ESI-MS/MS Determination of Adenosine in Human Plasma

HILIC-MS/MS Analysis of Adenosine in Patient Blood

Adenosine is a purine ribonucleoside with important roles in various physiological processes. A number of studies have indicated the importance of adenosine in cardiovascular diseases including syncope; however, the accurate determination of adenosine in human blood is challenging due to the molecule’s instability. In the present study, we report a simple method for the pre-treatment of blood samples and the development of a fast and efficient hydrophilic interaction chromatographic tandem mass spectrometry method for the analysis of adenosine in patient blood. During collection, samples were mixed directly with a solvent mixture containing 95% acetonitrile and 10 mM ammonium formate in a Vacutainer tube, resulting in successful prevention of adenosine metabolic processes and direct blood sample deproteinization. The method was validated according to bioanalytical industry guidelines and found to be accurate, repeatable, specific and sensitive with LLOQ 0.005 μg/mL, thus allowing its application in the analysis of real clinical samples.

[Basic Study on Organic Electron Transfer Reactions by Electrochemistry Combined with Quantum Chemical Calculations]

This review summarizes the results of the author's basic research on organic electrochemistry conducted at Gifu Pharmaceutical University over about 40 years. After completing graduate school, the author became a research associate in Prof. Tanekazu Kubota's laboratory and started research on molecular spectroscopy in 1983. After Prof. Kubota retired in 1989, the author continued investigations in the field of organic electrochemistry as an independent researcher. At that time, a research environment in which ab initio molecular orbital calculations can be used as an analytical tool for experimental research was developed, and the author commenced research on organic electrochemistry combined with quantum chemical calculations as a lifework. The author's research topics were basic research on the molecular theory of redox potentials of organic molecules, molecular design of functional molecules, intermolecular interactions of organic molecules involving electron transfers and electron transfer systems composed of bioactive quinones, and analytical application research based on the basic electrochemistry. In this review article, the essence of the research results is introduced while reflecting on the existing situation at the time of the research. The author concludes the review by expressing gratitude to all colleagues for supporting the research in the author's laboratory.

Adenosine-imprinted magnetic core-shell polyvinylbutyral microbeads for quantification of adenosine in plasma

Adenosine is an important molecule in the human body because it participates various biochemical processes, signalling in the physiological processes, and neurological disorders. In the current study, the surface imprinting method was used to prepare adenosine-imprinted magnetic core-shell polyvinylbutyral microbeads. These microbeads were utilized for quantification of adenosine in aqueous solution and control plasma in the range of 1-200 µM. The limit of detection was found to be 1.9 nM, which is quite sensitive compared with to some earlier studies. Fourier transform infrared spectroscopy, scanning electron microscopy, and a Zetasizer (particle size analyzer) were used for characterization of the prepared imprinted microbeads. To determine the efficiency of this method, selectivity experiments were conducted with adenosine-imprinted and non-imprinted magnetic core-shell polyvinylbutyral microbeads and with the competitive nucleosides cytidine, uridine, guanosine, and thymidine. Thermodynamic and kinetic studies were performed to assess adsorption of adenosine onto the adenosine-imprinted magnetic core-shell polyvinylbutyral microbeads from adenosine solution. The efficiency was linked to the specific surface reactivity, polarity and porosity of the imprinted microbeads.

Identification of new trace related impurities in adenosine products using ultra-high-performance liquid chromatography/electrospray ionization quadrupole time-of-flight tandem mass spectrometry

RATIONALE

Adenosine can induce various physiopathological effects and has been adopted as a drug to treat certain forms of supraventricular tachycardia. Adenosine is predominantly produced via fermentation that may generate many other bioactive compounds with similar structures at trace levels. Thus, it is necessary to identify these trace structurally related impurities. A new method using ultra-high-performance liquid chromatography (UHPLC) coupled with quadrupole time-of-flight tandem mass spectrometry (QTOF-MS/MS) is proposed to separate complex components at trace amounts; to obtain accurate mass measurements providing the elemental composition of unknown compounds; and MS/MS spectra for elucidation of structures.

METHODS

A UHPLC/QTOF-MS method was developed to separate and detect trace related impurities with structures similar to adenosine in formation samples. MS and MS/MS spectra of the impurities detected in real samples were acquired and used to propose their structures. Available reference standards were used to confirm the identification of some of the impurities detected.

RESULTS

Nine trace impurities of adenosine were separated and characterized. Of these nine, five were confirmed as 5'-adenylic acid, hypoxanthine, inosine, adenine, and 2'-deoxyadenosine by comparison with their available reference standards. The remaining four were proposed to be ADP-ribose, two S-epimers of 5'-deoxy-5'-methylsulfinyl adenosine, and 3'-α-glucosyl adenosine based on their MS and MS/MS spectra, and available literature. Additionally, the MS/MS fingerprints of the monosaccharide glycosyl groups were discovered and discussed.

CONCLUSIONS

A UHPLC/QTOF-MS method was established and used for the separation and characterization of nine trace related impurities of adenosine. Their structures were identified based on the MS and MS/MS spectra and retention times. In addition, the specific MS/MS fingerprints of the monosaccharide glycosyl moieties of the adenosine impurity analogs were summarized.

Accurate measurement of endogenous adenosine in human blood

Accurate determination of in vivo circulating concentrations of extracellular adenosine in blood samples is challenging due to the rapid formation and rapid clearance of adenosine in blood. A blood collection protocol was developed based on direct sampling of venous blood into, and instant mixing with, a STOP solution developed to conserve in vivo adenosine concentrations by completely preventing both its formation and clearance in collected blood. Stable isotope labeled AMP and adenosine spiked into blood ex vivo were used in combination with mass spectrometry to evaluate conservation of adenosine and prevention of its formation. A number of approved drugs, including the P2Y₁₂ antagonist ticagrelor, have been described to increase extracellular adenosine. This may contribute to its clinical profile, highlighting the importance of accurate measurement of in vivo adenosine concentrations.A high sensitive ultra performance liquid chromatography–tandem- mass spectrometry (UPLC-tandem-MS) analytical method for plasma adenosine was developed and validated with a lower limit of quantification of 2 nmol/L. The method demonstrated plasma adenosine stability during sample processing and analytical method performance relevant to human blood samples. The final STOP solution proved able to conserve exogenous adenosine and to prevent adenosine formation from exogenous AMP added in vitro to human blood over 15 minutes. The mean endogenous adenosine concentration in plasma prepared from venous blood collected from 10 healthy volunteers was 13 ± 7 nmol/L. Finally, the method was used to demonstrate the previously described concentration-dependent ability of ticagrelor to conserve extracellular adenosine at clinically relevant exposures. In conclusion, we report an optimized sampling protocol and a validated analytical method for accurate measurement of in vivo circulating adenosine concentrations in human blood, suitable for use in clinical trials.

Hyperbranched Polyglycerol Functionalized Silica Stationary Phase for Hydrophilic Interaction Liquid Chromatography

Surface-initiated anionic-ring-opening multibranching polymerization was employed to prepare a hyperbranched polyglycerol (HPG) functionalized silica stationary phase for hydrophilic interaction liquid chromatography (HILIC). The obtained stationary phase was characterized by Fourier-transform infrared spectrometry (FT-IR) and thermogravimetric analysis (TGA). The chromatographic properties of the prepared stationary phase were systematically investigated. The abundance and multitude distribution of hydroxyl groups in HPG endowed the stationary phase with improved hydrophilicity and enhanced separation performance compared with the stationary phase functionalized with monolayer of hydroxyl groups. The stationary phase showed excellent retention of various polar compounds, such as nucleosides, necleobases, phenols and sulfanilamides, indicating great potential in the separation of complex biosamples.